Chapter 12: Q25P (page 328)
Question: (I) Estimate the number of octaves in the human audible range, 20 Hz to 20 kHz.
The number of octaves in the human audible range is 10.
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Question: (II) (a) Determine the length of an open organ pipe that emits middle C (262 Hz) when the temperature is 18°C. (b) What are the wavelength and frequency of the fundamental standing wave in the tube? (c) What are \(\lambda \)and f in the traveling sound wave produced in the outside air?
Question: (III) When a player’s finger presses a guitar string down onto a fret, the length of the vibrating portion of the string is shortened, thereby increasing the string’s fundamental frequency (see Fig. 12–36). The string’s tension and mass per unit length remain unchanged. If the unfingered length of the string is l= 75.0 cm, determine the positions x of the first six frets, if each fret raises the pitch of the fundamental by one musical note compared to the neighboring fret. On the equally tempered chromatic scale, the ratio of frequencies of neighboring notes is 21/12.
Figure 12-36
Question: In audio and communications systems, the gain, \(\beta \) in decibals is defined for an amplifer as,
\(\beta = {\bf{10log}}\left( {\frac{{{P_{{\bf{out}}}}}}{{{P_{{\bf{in}}}}}}} \right)\)
Where \({P_{{\bf{in}}}}\) is the power input to the system and \({P_{{\bf{out}}}}\) is the power output. (a) A particular amplifer puts out 135 W of power for and input of 1.0 mW. What is its gain in dB? (b) if a signal to noise ratio of 93 dB is specified, what is the noise power if the output signal is 10 W?
Figure 12–32 shows various positions of a child on a swing moving toward a person on the ground who is blowing a whistle. At which position, A through E, will the child hear the highest frequency for the sound of the whistle? Explain your reasoning.
If a wind is blowing, will this alter the frequency of the sound heard by a person at rest with respect to the source? Is the wavelength or velocity changed?
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